which is more efficient?

I'm going to buy an air conditioner and am trying to figure out which has a lower operating cost. The AC that is 110 volts or the AC that is 220 volts. The 110 is 15,000 BTU and the 220 is 18,000 BTU, but lets just pretend they are exactly the same BTU.

Is the 220 more energy efficient because it uses less amps or are they exactly the same?

Other things being equal, they consume the same WATTS, which is what you pay for. 10 amps at 120 volts is 1200 watts. 5 amps at 240 is also 1200 watts. There are some advantages like for the same KW energy usage, you could use smaller wires, and since given same wire size, the higher amp unit would produce more heat ( I-squared_R) , and heat is wasted energy.

In the case of a window air conditioner, none of the above would be anything to lose sleep over.

I'm going to buy an air conditioner and am trying to figure out which has a lower operating cost.
The 110 is 15,000 BTU and
the 220 is 18,000 BTU
Is the 220 more energy efficient because it uses less amps or are they exactly the same?